Training Course
Aortic aneurysm Atul Mathur, Varun Mohan, Deepak Ameta, Gaurav Bhardwaj, Pradeep Haranahalli Department of Interventional Cardiology, Fortis Escorts Heart Institute, New Delhi, India
DEFINITION Aortic aneurysm refers to pathologic dilatation of aortic segment that has the tendency to expand and rupture. The extent of dilatation is debatable but one criterion is an increase in the diameter of at least 50% greater than that expected for the same aortic segment in unaffected individuals of same age and sex. Aortic aneurysms are described in terms of their size, location, morphology, and cause.
EPIDEMIOLOGY
Address for Correspondence: Dr. Gaurav Bhardwaj, Consultant, Department of Interventional Cardiology, Fortis Escorts Heart Institute, New Delhi, India. Email: [email protected]
Access this article online Website: www.intern-med.com DOI: 10.1515/jtim-2016-0008 Quick Response Code:
Prevalence The incidence of abdominal aortic aneurysms (AAAs) has increased during the past two decades, due in part to the aging of the population, the rise in the number of smokers, the introduction of screening programs, and improved diagnostic tools. The disorder is more common in men than in women, with prevalence rates estimated at 1.3–8.9% in men and 1.0–2.2% in women. [1] However, thoracic aortic aneurysms (TAAs) have an estimated incidence of at least 5-10 per 100,000 person-years. [2] According to location, TAAs are classified into aortic root or ascending aortic aneurysms, which are most common (≈60%), followed by aneurysms of the descending aorta (≈35%) and aortic arch (70
Rupture risk (%) 0 1 1–11 10–22 30–33
Other factors that have been associated with an increased risk of AAA rupture across several studies include female gender, smoking, hypertension, AAA expansion rate, and peak AAA wall stress. Individual studies have suggested an increased risk of AAA rupture for patients with rapid increase in intraluminal thrombus, increased AAA wall stiffness, increased wall tension, low forced expiratory volume in 1 second (FEV1) and for transplant patients.[11] For TAAs, mean rate of rupture or dissection was 2% per year for aneurysms smaller than 5 cm in diameter, 3% per year for those 5.0–5.9 cm, and 7% per year for those 6.0 cm or larger. Sex and body surface area may also play an important role in predicting complications of aneurysms. [9,12] Some have proposed using aortic cross-sectional area and body height.[12] Aortic risk calculator uses height, weight, and aortic size to calculate a yearly risk of rupture or dissection.[13] Patients with an aortic size index (ASI) of less than 2.75 cm/m² had a complication rate of 4%, those with an ASI between 2.75 and 4.25 cm/m² had an event 36
The incidence of new AAA after a single normal scan at 65 years is rare and, when present, rarely reaches a significant size. Screening should be considered at an earlier age for those at higher risk for AAA. In 2005, the U.S. Preventive Services Task Force recommended a one-time ultrasound screening for AAAs in men aged 65–75 years with a history of smoking.[15,16] The Society for Vascular Surgery recommends a one-time screening for AAAs in all men older than 65 years or as early as 55 years in men and women with a family history of AAAs.[16]
ANEURYSM GROWTH AND SURVEILLANCE Small AAAs (3.0–5.4 cm in diameter), when identified, should be monitored for expansion. In accordance with Laplace’s law, the larger the aneurysm, the higher is the rate of expansion. Current guidelines regarding the frequency of monitoring are as follows: for aneurysms with a diameter of 3.0–3.4 cm, every 3 years; 3.5–4.4 cm, yearly; and 4.5–5.4 cm, every 6 months.[17]
CLINICAL PRESENTATION Unruptured aortic aneurysms Unruptured aneurysms are generally asymptomatic in most patients. They are essentially diagnosed incidentally during clinical examination or during population screening. Nonruptured aneurysms might exceptionally be diagnosed after complications, such as distal embolization and, even more rarely, acute thrombosis. Minor and less specific symptoms include chronic vague abdominal and back pain, which can result from direct pressure on structures or by distension of visceral organs. Recent onset of severe lumbar pain has been deemed to indicate impending rupture. Ureterohydronephrosis might also take place, especially if the aneurysm is inflammatory or involves the iliac bifurcation. Similarly, most patients with a TAA are asymptomatic, and the aneurysm is discovered incidentally on chest radiography, echocardiography, CT,
JOURNAL OF TRANSLATIONAL INTERNAL MEDICINE / JAN-MAR 2016 / VOL 4 | ISSUE 1
Mathur et al.: Aortic Aneurysm
or MRI. Findings on physical examination such as aortic regurgitation may lead to further imaging and diagnosis of TAA. Symptoms of TAAs are usually related to a local mass effect, progressive aortic regurgitation, heart failure from aortic root dilation, or systemic embolization as a result of mural thrombus or atheroembolism. Ruptured abdominal aortic aneurysms Rupture of AAAs is heralded by the triad of sudden onset of pain in the mid-abdomen or flank (that may radiate into the scrotum), shock, and the presence of a pulsatile abdominal mass. However, the degree of shock varies according to the location and size of the rupture and the delay before the patient is examined. Rupture from the anterolateral wall into the peritoneal cavity (Figure 1) is usually dramatic and most often associated with death at the scene. Most patients with a rupture who reach the hospital alive have a rupture of the posterolateral wall of aneurysm into the retroperitoneal space; a small tear can temporarily seal the rupture and the initial blood loss might be small. This initial event is systematically followed within hours by a larger rupture. This biphasic evolution emphasizes the importance of the intermediate period after the initial event, which should be used for medical transfer and emergency repair. Anecdotically, the first episode of rupture could be definitely contained and become a chronic pulsatile extra-aortic hematoma. Very rarely, the aneurysm might spontaneously rupture into the duodenum (Figure 1); an incidence rate at necropsy of 0.04–0.07% has been
reported.[18] More often, aortoduodenal fistula can occur after previous repair, with an incidence rate of 0.5–2.3%.[19] Rupture into the vena cava can also take place with an apparent pattern of lower extremity edema erroneously attributed to cavoiliac thrombophlebitis. However, the development of high-output congestive heart failure and the perception of continuous abdominal noise is pathognomonic. The overall prevalence of aortocaval fistula is 3–6% of all ruptured aortic aneurysms.[20] Thoracic aortic rupture leads to sudden severe chest or back pain. Rupture into the pleural cavity (usually left) or into the mediastinum is associated with hypotension, rupture into the esophagus leads to hematemesis from an aortoesophageal fistula, and rupture into the bronchus or trachea results in hemoptysis. Infected TAAs are more commonly associated with fistulas. Acute aortic expansion, contained rupture, and pseudoaneurysm can cause severe chest or back pain. Thoracic aortic dissection is more common than rupture.
TREATMENT Risk factor modification Smoking cessation is associated with reduced rate of aneurysmal growth. The recognized association between either hypertension or hypercholesterolemia and the occurrence of abdominal aortic aneurysm suggests that control of these coexisting conditions with medications such as antihypertensive agents and statins may decrease the risk, although limited data are available to support this hypothesis. Patients with small aneurysms should be encouraged to exercise regularly because moderate physical activity does not adversely influence the risk for rupture and may even limit the rate of aneurysm growth. Medical therapy Several drugs have been evaluated for their potential to limit AAA. Betablockers, antibiotics, and anti-inflammatory agents have been examined in randomized trials, and angiotensin-converting-enzyme inhibitors, angiotensinreceptor blockers, statins, and antiplatelet agents have been examined in nonrandomized studies. Unfortunately, none of these drugs have been shown to provide a benefit.[21] Doxycycline inhibits matrix metalloproteinases, a finding that suggests that it might reduce the growth of aneurysms. However, in a placebo-controlled, randomized trial, doxycycline at a daily dose of 100 mg did not reduce the growth of small aneurysms over a follow-up period of 18 months.[22]
Figure 1: Different possible sites of rupture of an abdominal aortic aneurysm. 1: Anterolateral free rupture in the abdominal cavity. 2: Retroperitoneal rupture. 3: Rupture of retroperitoneal sac. 4: Rupture into the duodenum. 5: Rupture into the inferior vena cava.
Indications for aneurysm repair The management of aneurysm depends on the size or diameter of the aneurysm and is a balance between the
JOURNAL OF TRANSLATIONAL INTERNAL MEDICINE / JAN-MAR 2016 / VOL 4 | ISSUE 1
37
Mathur et al.: Aortic Aneurysm
risk of aneurysm rupture and the operative mortality for aneurysm repair. For very small aneurysms, 3.0–3.9 cm, the risk of rupture is negligible. Therefore, these aneurysms do not require surgical intervention and should be kept under ultrasound surveillance at regular intervals. For aneurysms between 4 and 5.5 cm in diameter, rapid growth (>1 cm/year) and the development of symptoms referable to the aneurysm warrant intervention. Aneurysm repair should be considered at a maximum aneurysm diameter of 5.2 cm in females and 5.5 cm in males. This is because females appear more likely to suffer AAA rupture at smaller aortic diameters than males.[23] In general, surgical replacement of ascending aorta should be performed when the ascending aortic diameter reaches 5.5 cm and, in the setting of BAV aneurysm, MFS, and familial TAA syndromes, when it reaches 5 cm.[11,12] In adults with LDS, surgery is recommended when the aortic root measures 4.2 cm by transesophageal echocardiogram (TEE) or 4.4–4.6 cm by CT or MRI,[11] although some experts recommend surgery in patients with LDS once the aortic root is larger than 4 cm.[24,25] In TS, prophylactic surgery should be considered when the ascending aorta is 3.5 cm or larger or 2.5 cm/m2 or larger.[26] Surgical timing also depends on the family history, sex, rate of aneurysm growth, body size, coexisting aortic valve disease, need for other heart surgery, comorbid conditions, and patient and physician preference.
INTERVENTIONS FOR ANEURYSM REPAIR Endovascular aneurysm repair Endovascular aneurysm repair (EVAR) is a minimally invasive procedure for the treatment of AAA based on the
use of a stent graft, usually deployed inside the aneurysm through femoral access to exclude the AAA sac from the circulation. EVAR requires adequate aortic and iliac fixation sites for effective sealing and fixation. Potential advantages of EVAR over open repair include reduced operative time, avoidance of general anesthesia, less trauma and postoperative pain, reduced hospital stay and less need for intensive care unit (ICU), reduced blood loss, and reduced postoperative mortality. Potential disadvantages include the risk of incomplete AAA sealing, with the development of continuous refilling of the aneurysm sac, either because the graft does not seal completely at the extremities (Type I endoleak), between segments (Type III endoleak), or because of backfilling of the aneurysm from other small vessels in the aneurysm wall (Type II endoleak). Morphological criteria for EVAR are shown in Table 2. Graft model choice Appropriately sized aortic endograft should be selected on the basis of patient anatomy: according to the instruction for use of abdominal endografts, generally, the device should be oversized 15–20% with respect to the aortic neck diameter to guarantee optimal seal. Management of concomitant iliac aneurysms Concomitant iliac aneurysms may be present in up to 40% of patients with EVAR. Coil embolization of hypogastric (internal iliac) artery, followed by endograft extension into the external iliac artery (EIA), is usually performed to prevent Type II endoleak. Hypogastric embolization is usually preferred over simple coverage of its ostium by the endograft to prevent the risk of Type II endoleak, but coils should be placed as proximal as possible to spare collateral circulation. Approximately one-third of patients with hypogastric occlusion have symptoms of pelvic ischemia: buttock
Table 2: Morphological criteria for EVAR Proximal aortic neck Neck diameter >17 mm, < 32 mm Angle between the suprarenal aorta and the juxtarenal aorta < 60° Angle between the juxtarenal aorta and the long axis of the aneurysm sac 10 mm Neck thrombus covering
Aortic aneurysm Atul Mathur, Varun Mohan, Deepak Ameta, Gaurav Bhardwaj, Pradeep Haranahalli Department of Interventional Cardiology, Fortis Escorts Heart Institute, New Delhi, India
DEFINITION Aortic aneurysm refers to pathologic dilatation of aortic segment that has the tendency to expand and rupture. The extent of dilatation is debatable but one criterion is an increase in the diameter of at least 50% greater than that expected for the same aortic segment in unaffected individuals of same age and sex. Aortic aneurysms are described in terms of their size, location, morphology, and cause.
EPIDEMIOLOGY
Address for Correspondence: Dr. Gaurav Bhardwaj, Consultant, Department of Interventional Cardiology, Fortis Escorts Heart Institute, New Delhi, India. Email: [email protected]
Access this article online Website: www.intern-med.com DOI: 10.1515/jtim-2016-0008 Quick Response Code:
Prevalence The incidence of abdominal aortic aneurysms (AAAs) has increased during the past two decades, due in part to the aging of the population, the rise in the number of smokers, the introduction of screening programs, and improved diagnostic tools. The disorder is more common in men than in women, with prevalence rates estimated at 1.3–8.9% in men and 1.0–2.2% in women. [1] However, thoracic aortic aneurysms (TAAs) have an estimated incidence of at least 5-10 per 100,000 person-years. [2] According to location, TAAs are classified into aortic root or ascending aortic aneurysms, which are most common (≈60%), followed by aneurysms of the descending aorta (≈35%) and aortic arch (70
Rupture risk (%) 0 1 1–11 10–22 30–33
Other factors that have been associated with an increased risk of AAA rupture across several studies include female gender, smoking, hypertension, AAA expansion rate, and peak AAA wall stress. Individual studies have suggested an increased risk of AAA rupture for patients with rapid increase in intraluminal thrombus, increased AAA wall stiffness, increased wall tension, low forced expiratory volume in 1 second (FEV1) and for transplant patients.[11] For TAAs, mean rate of rupture or dissection was 2% per year for aneurysms smaller than 5 cm in diameter, 3% per year for those 5.0–5.9 cm, and 7% per year for those 6.0 cm or larger. Sex and body surface area may also play an important role in predicting complications of aneurysms. [9,12] Some have proposed using aortic cross-sectional area and body height.[12] Aortic risk calculator uses height, weight, and aortic size to calculate a yearly risk of rupture or dissection.[13] Patients with an aortic size index (ASI) of less than 2.75 cm/m² had a complication rate of 4%, those with an ASI between 2.75 and 4.25 cm/m² had an event 36
The incidence of new AAA after a single normal scan at 65 years is rare and, when present, rarely reaches a significant size. Screening should be considered at an earlier age for those at higher risk for AAA. In 2005, the U.S. Preventive Services Task Force recommended a one-time ultrasound screening for AAAs in men aged 65–75 years with a history of smoking.[15,16] The Society for Vascular Surgery recommends a one-time screening for AAAs in all men older than 65 years or as early as 55 years in men and women with a family history of AAAs.[16]
ANEURYSM GROWTH AND SURVEILLANCE Small AAAs (3.0–5.4 cm in diameter), when identified, should be monitored for expansion. In accordance with Laplace’s law, the larger the aneurysm, the higher is the rate of expansion. Current guidelines regarding the frequency of monitoring are as follows: for aneurysms with a diameter of 3.0–3.4 cm, every 3 years; 3.5–4.4 cm, yearly; and 4.5–5.4 cm, every 6 months.[17]
CLINICAL PRESENTATION Unruptured aortic aneurysms Unruptured aneurysms are generally asymptomatic in most patients. They are essentially diagnosed incidentally during clinical examination or during population screening. Nonruptured aneurysms might exceptionally be diagnosed after complications, such as distal embolization and, even more rarely, acute thrombosis. Minor and less specific symptoms include chronic vague abdominal and back pain, which can result from direct pressure on structures or by distension of visceral organs. Recent onset of severe lumbar pain has been deemed to indicate impending rupture. Ureterohydronephrosis might also take place, especially if the aneurysm is inflammatory or involves the iliac bifurcation. Similarly, most patients with a TAA are asymptomatic, and the aneurysm is discovered incidentally on chest radiography, echocardiography, CT,
JOURNAL OF TRANSLATIONAL INTERNAL MEDICINE / JAN-MAR 2016 / VOL 4 | ISSUE 1
Mathur et al.: Aortic Aneurysm
or MRI. Findings on physical examination such as aortic regurgitation may lead to further imaging and diagnosis of TAA. Symptoms of TAAs are usually related to a local mass effect, progressive aortic regurgitation, heart failure from aortic root dilation, or systemic embolization as a result of mural thrombus or atheroembolism. Ruptured abdominal aortic aneurysms Rupture of AAAs is heralded by the triad of sudden onset of pain in the mid-abdomen or flank (that may radiate into the scrotum), shock, and the presence of a pulsatile abdominal mass. However, the degree of shock varies according to the location and size of the rupture and the delay before the patient is examined. Rupture from the anterolateral wall into the peritoneal cavity (Figure 1) is usually dramatic and most often associated with death at the scene. Most patients with a rupture who reach the hospital alive have a rupture of the posterolateral wall of aneurysm into the retroperitoneal space; a small tear can temporarily seal the rupture and the initial blood loss might be small. This initial event is systematically followed within hours by a larger rupture. This biphasic evolution emphasizes the importance of the intermediate period after the initial event, which should be used for medical transfer and emergency repair. Anecdotically, the first episode of rupture could be definitely contained and become a chronic pulsatile extra-aortic hematoma. Very rarely, the aneurysm might spontaneously rupture into the duodenum (Figure 1); an incidence rate at necropsy of 0.04–0.07% has been
reported.[18] More often, aortoduodenal fistula can occur after previous repair, with an incidence rate of 0.5–2.3%.[19] Rupture into the vena cava can also take place with an apparent pattern of lower extremity edema erroneously attributed to cavoiliac thrombophlebitis. However, the development of high-output congestive heart failure and the perception of continuous abdominal noise is pathognomonic. The overall prevalence of aortocaval fistula is 3–6% of all ruptured aortic aneurysms.[20] Thoracic aortic rupture leads to sudden severe chest or back pain. Rupture into the pleural cavity (usually left) or into the mediastinum is associated with hypotension, rupture into the esophagus leads to hematemesis from an aortoesophageal fistula, and rupture into the bronchus or trachea results in hemoptysis. Infected TAAs are more commonly associated with fistulas. Acute aortic expansion, contained rupture, and pseudoaneurysm can cause severe chest or back pain. Thoracic aortic dissection is more common than rupture.
TREATMENT Risk factor modification Smoking cessation is associated with reduced rate of aneurysmal growth. The recognized association between either hypertension or hypercholesterolemia and the occurrence of abdominal aortic aneurysm suggests that control of these coexisting conditions with medications such as antihypertensive agents and statins may decrease the risk, although limited data are available to support this hypothesis. Patients with small aneurysms should be encouraged to exercise regularly because moderate physical activity does not adversely influence the risk for rupture and may even limit the rate of aneurysm growth. Medical therapy Several drugs have been evaluated for their potential to limit AAA. Betablockers, antibiotics, and anti-inflammatory agents have been examined in randomized trials, and angiotensin-converting-enzyme inhibitors, angiotensinreceptor blockers, statins, and antiplatelet agents have been examined in nonrandomized studies. Unfortunately, none of these drugs have been shown to provide a benefit.[21] Doxycycline inhibits matrix metalloproteinases, a finding that suggests that it might reduce the growth of aneurysms. However, in a placebo-controlled, randomized trial, doxycycline at a daily dose of 100 mg did not reduce the growth of small aneurysms over a follow-up period of 18 months.[22]
Figure 1: Different possible sites of rupture of an abdominal aortic aneurysm. 1: Anterolateral free rupture in the abdominal cavity. 2: Retroperitoneal rupture. 3: Rupture of retroperitoneal sac. 4: Rupture into the duodenum. 5: Rupture into the inferior vena cava.
Indications for aneurysm repair The management of aneurysm depends on the size or diameter of the aneurysm and is a balance between the
JOURNAL OF TRANSLATIONAL INTERNAL MEDICINE / JAN-MAR 2016 / VOL 4 | ISSUE 1
37
Mathur et al.: Aortic Aneurysm
risk of aneurysm rupture and the operative mortality for aneurysm repair. For very small aneurysms, 3.0–3.9 cm, the risk of rupture is negligible. Therefore, these aneurysms do not require surgical intervention and should be kept under ultrasound surveillance at regular intervals. For aneurysms between 4 and 5.5 cm in diameter, rapid growth (>1 cm/year) and the development of symptoms referable to the aneurysm warrant intervention. Aneurysm repair should be considered at a maximum aneurysm diameter of 5.2 cm in females and 5.5 cm in males. This is because females appear more likely to suffer AAA rupture at smaller aortic diameters than males.[23] In general, surgical replacement of ascending aorta should be performed when the ascending aortic diameter reaches 5.5 cm and, in the setting of BAV aneurysm, MFS, and familial TAA syndromes, when it reaches 5 cm.[11,12] In adults with LDS, surgery is recommended when the aortic root measures 4.2 cm by transesophageal echocardiogram (TEE) or 4.4–4.6 cm by CT or MRI,[11] although some experts recommend surgery in patients with LDS once the aortic root is larger than 4 cm.[24,25] In TS, prophylactic surgery should be considered when the ascending aorta is 3.5 cm or larger or 2.5 cm/m2 or larger.[26] Surgical timing also depends on the family history, sex, rate of aneurysm growth, body size, coexisting aortic valve disease, need for other heart surgery, comorbid conditions, and patient and physician preference.
INTERVENTIONS FOR ANEURYSM REPAIR Endovascular aneurysm repair Endovascular aneurysm repair (EVAR) is a minimally invasive procedure for the treatment of AAA based on the
use of a stent graft, usually deployed inside the aneurysm through femoral access to exclude the AAA sac from the circulation. EVAR requires adequate aortic and iliac fixation sites for effective sealing and fixation. Potential advantages of EVAR over open repair include reduced operative time, avoidance of general anesthesia, less trauma and postoperative pain, reduced hospital stay and less need for intensive care unit (ICU), reduced blood loss, and reduced postoperative mortality. Potential disadvantages include the risk of incomplete AAA sealing, with the development of continuous refilling of the aneurysm sac, either because the graft does not seal completely at the extremities (Type I endoleak), between segments (Type III endoleak), or because of backfilling of the aneurysm from other small vessels in the aneurysm wall (Type II endoleak). Morphological criteria for EVAR are shown in Table 2. Graft model choice Appropriately sized aortic endograft should be selected on the basis of patient anatomy: according to the instruction for use of abdominal endografts, generally, the device should be oversized 15–20% with respect to the aortic neck diameter to guarantee optimal seal. Management of concomitant iliac aneurysms Concomitant iliac aneurysms may be present in up to 40% of patients with EVAR. Coil embolization of hypogastric (internal iliac) artery, followed by endograft extension into the external iliac artery (EIA), is usually performed to prevent Type II endoleak. Hypogastric embolization is usually preferred over simple coverage of its ostium by the endograft to prevent the risk of Type II endoleak, but coils should be placed as proximal as possible to spare collateral circulation. Approximately one-third of patients with hypogastric occlusion have symptoms of pelvic ischemia: buttock
Table 2: Morphological criteria for EVAR Proximal aortic neck Neck diameter >17 mm, < 32 mm Angle between the suprarenal aorta and the juxtarenal aorta < 60° Angle between the juxtarenal aorta and the long axis of the aneurysm sac 10 mm Neck thrombus covering
